Portable digital devices such as PDA, notebooks, or cellular phones now combine several small memory cards to serve as the semiconductor storage media. The present prevailing specifications include CF (Compact Flash), SD (Security Digital), MMC (Multimedia Card), Smart Media and Memory Stick, etc. In order to expand the I/O (input-output) applications in the host system of the aforesaid portable digital devices such as input and output of image files or wireless transmission, some vendors have developed an IO card (input-output card) to further improve CF, SD and Memory Stick.
With the gradually increased retrieval memory capacity, the demand for additional memory of the IO card also grows.
One of the conventional methods for solving this problem is to add extra insertion slots on the host system to accommodate the memory card. FIG. 1 illustrates such an approach. The host system 100 has two insertion slots 101 and 102 to receive an IO card 103 and a memory card 104 respectively. However, since adding more insertion slots on the host systems also increases the size and cost, miniaturization is the trend for designing portable digital devices. Thus, since it is essential to reduce the number of insertion slots, there is a need to integrate the IO card and the memory card. Furthermore, multiple insertion slots incur another problem. Since the data transmission between the IO card 103 and the memory card 104 has to go through the data bus inside the host system 100, it is not possible to achieve a desirable transmitting efficiency.
The Combo card, which directly expands the memory capacity of the IO card, is one of the products that integrate the IO card and the memory card. However, since the integrated design limits the memory capacity, it cannot be replaced with a larger capacity memory card.
In order to expand the memory capacity without having additional insertion slots, Sandisk Co. and Socket Communication Co. together have disclosed a patent WO 02/19266 A2, in which they provide a data transmission method of connecting a non-volatile memory card of a host system to an external device. Their method includes an electrical and mechanical connection between the IO card and the memory card, and a data transmission between the memory card and the external device through the IO card. The IO card in the disclosed embodiment is a wireless transmitting card to provide radio transmission between the memory card and the external device.
The embodiment of the patent mentioned above is depicted in FIG. 2. A memory card 202 is inserted into an insertion slot 201 of a host system 200 while an IO card 203 is inserted into a tail end of the memory card 202 to establish the mechanical and electrical connection. Hence, data in the IO card 203 may be transmitted to the host system 200 through the memory card 202. As a result, the IO card and the memory card are integrated to have only one insertion slot.
However, in such a structure of data transmission, the function of the IO card controller is more complex than the memory card controller. Additional functions have to be added to the memory card controller to transmit data between the IO card and memory card and host system. Moreover, because the tail end of the memory card has to establish mechanical and electrical connection with the IO card, the memory card not only has to be made with specially specified dimensions, it is also not replaceable or interchangeable with the memory cards now available on the market.
In terms of performance, due to the performance differences between the controllers of the IO card and the memory card, the overall data transmitting efficiency is lowered. This problem has become a bottleneck for transmitting data among the IO card with integrated memory card and the host system. Moreover, since the memory card cannot be replaced nor interchanged as desired, its capacity cannot be expanded.
Furthermore, the size of the IO card is usually greater than the size of the memory card. Thus, connecting the IO card to the tail end of the memory card reduces the total mechanical coupling strength.